Refrigeration apparatus and method for controlling the same

ABSTRACT

A refrigeration apparatus includes a condensing unit, a flow distributor, and an evaporator connected to the condensing unit via the flow distributor. A pressure detector is configured to detect condensation pressure of the refrigerant. A calculation unit is configured to calculate a target condensation pressure of refrigerant necessary for the refrigerant to be an evaporation temperature in the evaporator. A controller is configured to control the condensing unit so that the condensation pressure of the refrigerant becomes equal to or more than the target condensation pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of the U.S. patentapplication Ser. No. 11/319,698 filed Dec. 29, 2005, which claimspriority under 35 U.S.C. §119 to Japanese Patent Application No.2004-382995, filed Dec. 30, 2004. The contents of these applications areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a refrigeration apparatus, a method forcontrolling a refrigeration apparatus, and a computer readable media forcontrolling a computer.

2. Discussion of the Background

Generally, a refrigeration apparatus is provided with a condensationpressure adjustment valve, a fan controller and the like in a condenserof the refrigeration apparatus. The condensation temperature iscontrolled around 30° C. at the lowest limit, irrespective of theevaporation temperature of the refrigerant in or the outside temperatureof the unit cooler. In this respect, the present inventor hasdemonstrated that a higher efficiency and significant power savings canbe achieved by operating the refrigeration apparatus without controllingthe condensation pressure all year around. See “Energy-Saving Freezerand Refrigeration Equipment without Condensation Pressure Control”Refrigeration and Air Conditioning Equipment, Vol. 25, No. 6, pp. 17-25.June 1998. The contents of this reference are incorporated by referencein their entirety.

According to this reference, it is possible to operate the refrigerationapparatus at a very small pressure differential by allowing thecondensation temperature to follow the course of outside temperatureswithout controlling it around 30° C., and by selecting a flowdistributor based on the freezer performance and the refrigeranttemperature under a low condensation pressure.

More specifically, this involves the selection of nozzle diameter, tubediameter and tube length which will not allow the pressure drop in thenozzles and tubes of the distributor to fall below 70 kPa under theminimum condition for uniform refrigerant distribution in the unitcooler. As a result of this, refrigerant liquid will be uniformlydistributed to the various circuits in the unit cooler. By employingthis special design and operation approach, it is proven that theoperation becomes possible at a very small difference of 300 kPa betweenthe evaporation pressure and the condensation pressure of refrigerant.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a refrigerationapparatus includes a condensing unit, a flow distributor, and anevaporator connected to the condensing unit via the flow distributor. Apressure detector is configured to detect condensation pressure of therefrigerant. A calculation unit is configured to calculate a targetcondensation pressure of refrigerant necessary for the refrigerant to bean evaporation temperature in the evaporator. A controller is configuredto control the condensing unit so that the condensation pressure of therefrigerant becomes equal to or more than the target condensationpressure.

According to another aspect of the present invention, a method forcontrolling a refrigeration apparatus includes detecting condensationpressure of refrigerant, calculating a target condensation pressure ofthe refrigerant necessary for the refrigerant to be an evaporationtemperature in the evaporator, and controlling a condensing unitconnected to the evaporator via a flow distributor so that thecondensation pressure of the refrigerant becomes equal to or more thanthe target condensation pressure.

According to yet another aspect of the present invention, a computerreadable media for controlling a computer to perform the steps ofdetecting condensation pressure of refrigerant; calculating a targetcondensation pressure of the refrigerant necessary for the refrigerantto be an evaporation temperature in the evaporator; and controlling acondensing unit connected to the evaporator via a flow distributor sothat the condensation pressure of the refrigerant becomes equal to ormore than the target condensation pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a refrigeration apparatus according toan embodiment of the present invention;

FIG. 2 is a drawing showing the relationship between the evaporationtemperature of the refrigerant and the amount of pressure drop obtainedfrom the liquid temperature of the refrigerant (R-22);

FIG. 3 is a drawing showing the relationship between the evaporationtemperature of the refrigerant and the amount of pressure drop obtainedfrom the liquid temperature of the refrigerant (R-404a);

FIG. 4 is a schematic illustration of the condenser pressureoptimization controller; and

FIG. 5 is a flow chart for controlling the condensation pressure.

DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

The apparatus disclosed in the “Energy-Saving Freezer and RefrigerationEquipment without Condensation Pressure Control” does not consider thetemperature rise due to the load generated by stored products in theactual operation of unit cooler. For walk-in freezers, no considerationis given to the dryness of refrigerant, χ, which is induced by anincrease in freezing performance or rise in the refrigerant liquidtemperature, because the evaporation temperature goes up as the roomtemperature rises upon the completion of defrosting in actual operation.Thus, applying the background art as it is to refrigeration apparatusoperated under diverse conditions or allowing the condensation pressureto decrease following the outside air conditions may lead to anoperation failure due to the following problems.

Refrigeration equipment using R-22 as the refrigerant and a two-stagecompression freezing cycle at a displacement volume ratio of 2:1 betweenlow and high stages is hereby used as an example. The normal pressure isexpressed as the absolute pressure, abs. Under an outside temperature of−10° C., the condensation temperature of the refrigerant was at tk=−7°C. (converted to an equivalent pressure of 395 kPa (abs), which isapplicable to the subsequent items); the room temperature of therefrigerator at −35° C.; the evaporation temperature of refrigerant att0=−41° C. (100 kPa); and the liquid temperature t1=−25° C., thepressure drop in the flow distributor to the unit cooler was made 79 kPaby selecting appropriate nozzles and tubes.

The  condensation  pressure  of  refrigerant:  395  kPa  (abs) − pressure  loss  in  the  liquid  pipe:  26  kPa − pressure  drop  in  the  expansion  valve:  190  kPa − pressure  drop  in  the  flow  distributor:  79  kPa = evaporation  pressure:  100  kPa

As shown, at a freezer capacity Φo=15 kW, the condensation pressure hadan appropriate value necessary for the amount of pressure drop.

Under this operating condition, assuming that goods are brought into thefreezer room and that the thermal load from this causes the roomtemperature to rise to −23° C., the evaporation temperature ofrefrigerant would be t0=−12° C. (an equivalent pressure of 164 kPa(abs)); freezer capacity, Φo=23 kW; and the refrigerant liquidtemperature, T1=−12° C. Thus dryness χ and freezer capacity Φo areincreased. The pressure drop in the flow distributor, on the other hand,almost doubles to 150 kPa, with the pressure loss in the liquid pipingat 48 kPa and the pressure drop in the expansion valve at 265 kPa.

At this point, the sum of gross pressure loss and pressure drops is asfollows:

pressure  loss  in  the  refrigerant  liquid  piping:  48  kPa + pressure  drop  in  the  expansion  valve:  265  kPa + pressure  drop  in  the  flow  distributor:  150  kPa = 463  kPa.

When the evaporation pressure of 164 kPa (abs), the ultimate value aftersuch pressure drops, is added to the above, the total becomes 627 kPa,that is, the necessary condensation pressure. When converted to anequivalent temperature, this is +6.6° C., the limit for the condensationpressure.

On the other hand, since the outside temperature is set at −10° C. asabove, if the condensation pressure is allowed to follow the outsidetemperature, then the condensation temperature will drop down to about−7° C. As a result, the pressure drop necessary for refrigerant to reachthe evaporation pressure will not be attained; and even if the expansionvalve is fully opened, the refrigerant in the refrigerant side coil ofthe unit cooler will end up overheated. This leads to an abnormaloperating condition where the apparent freezing capacity of the unitcooler decreases, and the difference between the room temperature andthe evaporation temperature of refrigerant, TD, reaches 18° C. If, inthis condition, the evaporation temperature of the refrigerant is −41°C., the freezing capacity is 15 kW, and the freezing capacity is largerthan the thermal load of the storage room, then the temperature willeventually reach −35° C. as initially set. Freezers, on the other hand,have higher thermal loads and are susceptible to superheat when thethermal load is larger than the freezing capacity, resulting ininadequate cooling. It is therefore necessary to obtain a pressure droplarge enough to produce the appropriate evaporation pressure based onthe room temperature; the above-mentioned 627 kPa (abs) (equivalenttemperature of +6.6° C.) thus represents the value of condensationpressure required for normal operation.

If the compression side of the refrigeration equipment circuit, i.e.,the condensation pressure, decreases below the above-mentioned totalpressure value, which is the sum of the pressure losses and pressuredrops with the evaporation pressure as the other endpoint, then theoperation proposed here becomes impossible for the refrigeration cyclethat uses a pressure difference for circulation. Since equilibrium isreached at a low evaporation temperature, insufficient refrigerationperformance and inadequate cooling will occur.

In addition, when the unit cooler is restarted at a high temperatureafter defrosting, the evaporation temperature will be −20° C., even whenthe MOP (Maximum Operating Pressure) function is deployed; and thenecessary amount of pressure drop will temporarily reach approximately760 kPa due to increased freezing performance and higher refrigerantliquid temperature. For refrigerant distributors constructed with fixednozzles and tubes without any mechanism to control the rate ofrefrigerant flow, changes in the mass flow and the dryness χ ofrefrigerant will lead to large variations in the pressure drop.

For refrigeration apparatus designed with the temperature differentialbetween evaporation and condensation as its operating principle and 300kPa as the minimum necessary condition for refrigerant distribution totake place, the amount of pressure drop necessary to attain theevaporation temperature increases as the mass flow of refrigerant and/orthe liquid temperature increases. When allowed to follow the course ofoutside temperature, on the other hand, the operating conditiontypically presents a pressure drop below the required level. This makesit necessary to maintain the condensation pressure above the amount ofpressure drop required to reach the evaporation temperature, and if itfalls below the pressure drop value, then an equilibrium will be reachedwith the evaporation temperature differential at a very low point,causing the freezing performance of the refrigeration apparatus todeteriorate. This renders the freezer capacity extremely insufficientfor the load, causing poor cooling, and even an operation failure.

Refrigeration equipment using R-404A (Dew Point Formula) as therefrigerant and a two-stage compression freezing cycle at a displacementvolume ratio of 2.5:1 between low and high stages is hereby used asanother example. Under an outside temperature of −15° C., thecondensation temperature of the refrigerant at tk=−10° C. (equivalent to440 kPa (abs)), the room temperature of the refrigerator at −69° C., theevaporation temperature of refrigerant at t0=−71° C. (100 kPa), and theliquid temperature t1=−48° C., the required pressure drop in the flowdistributor upstream to the unit cooler is 66 kPa. At the same time, thepressure drop in the expansion valve is 260 kPa, pressure loss in theliquid piping is 30 kPa, and the freezing capacity is Φo=14 kW. Underthis operating condition, the door of the refrigeration apparatus wasopened to exchange the frozen goods with fresh unfrozen goods. As aresult, the temperature of the refrigeration apparatus rose to −40° C.,and the increased freezing performance resulted in a 5° C. difference TDbetween the evaporation temperature of the refrigerant in the unitcooler and the room temperature; the evaporation temperature rose to−45° C., and the freezing capacity increased to Φo=40 kW.

The appropriate amount of pressure drop to attain the evaporationtemperature under these conditions is as follows:

pressure  loss  in  the  liquid  pipe:  67  kPa + pressure  drop  in  the  expansion  valve:  220  kPa + pressure  drop  in  the  flow  distributor:  250  kPa = 537  kPa

When the evaporation pressure of 109 kPa (abs), which is the end pointof the pressure drop, is added to this, the required pressure is 646 kPa(abs). In terms of equivalent temperature, this represents +2° C., whichis the limit value for condensation pressure. If the condensationpressure is allowed to decrease following the outside temperature, itwill fall below the amount of pressure drop necessary to attain theevaporation temperature, resulting in the lowering of the evaporationpressure. As a result, only an extremely small freezing capacity isgenerated in relation to the thermal load, causing inadequate cooling.It is therefore necessary to maintain the condensation pressure abovethe required pressure drop. Even if the outside temperature is at −15°C., it is necessary to limit the condensation pressure at 646 kPa (abs)(the equivalent temperature of about +2° C.) so that the system operatesat the evaporation temperature of refrigerant t0=−45° C.

FIG. 1 shows a schematic diagram of a refrigeration apparatus accordingto an embodiment of the present invention. In this refrigerationapparatus, the temperature of liquid refrigerant is controlled accordingto different evaporation temperatures. Referring to FIG. 1, a unitcooler 13 has a fan 14, a fin coil (not shown), a flow distributor 15,and a suction head 18 for collecting pipes. The distributor 15 isconnected to each circuit in the fin coil through nozzle 16 and tube 17.The condensation pressure optimization controller 23 has, on the otherhand, a liquid temperature sensor 24, an evaporation temperature sensor25, a refrigerant temperature sensor 26, a temperature sensor 27 on theair inlet side of the unit cooler 13, a pressure sensor 28, and aninverter 12. The liquid temperature sensor 24 is for measuring therefrigerant temperature on the upstream side of the expansion valve 19.The refrigerant temperature sensor 26 is for measuring the refrigeranttemperature at the inlet port of the distributor 15. The pressure sensor28 is for measuring the refrigerant pressure on the upstream side of theexpansion valve 19. The expansion valve's superheat controller 20 isconnected to the expansion valve 19. The superheat controller 20 isconnected respectively to a temperature sensor 21 that measures therefrigerant gas temperature in the refrigerant suction pipe and apressure sensor 22 for the expansion valve that measures the saturationpressure. The expansion valve's superheat controller 20 regulates therefrigerant flow rate of the expansion valve by determining the degreeof superheat from the pressure-equivalent temperature and the actualmeasurement of the temperature sensor 21.

The air-cooled condenser 8, on the other hand, is equipped with a fan 9that is driven by a motor 10, which is in turn powered by the outputfrom the inverter 12. This inverter 12 is provided with power through anelectromagnetic switch 11 from a power source. The air condenser 8 hasits liquefied refrigerant outlet side connected to a refrigerant liquidreceiver 2 through a valve, while the refrigerant liquid receiver 2 hasits refrigerant outlet side connected to an intermediate cooler 3 via adryer 4. One of the refrigerant outlet ports of this intermediate cooler3 is connected to the expansion valve 19 after over-cooling, while theoutlet port to the high stage suction of the two-stage compressionfreezer unit 1. The intermediate cooler 3 is connected to the expansionvalve 5 for the intermediate cooler, a solenoid valve 6, and sight glass7.

FIG. 4 is a schematic illustration of the controller 23. In thisembodiment, the controller 23 is, for example, a computer system. Thecomputer system 23 implements the method of the present embodimentaccording to the invention, wherein the computer housing 102 houses amotherboard 104 which contains a CPU 106, memory 108 (e.g., DRAM, ROM,EPROM, EEPROM, SRAM, SDRAM, and Flash RAM), and other optional specialpurpose logic devices (e.g., ASICs) or configurable logic devices (e.g.,GAL and reprogrammable FPGA). The computer system 23 also includesplural input devices, (e.g., a keyboard 122 and mouse 124), and adisplay card 110 for controlling monitor 120. In addition, the computersystem 23 further includes a floppy disk drive 114; other removablemedia devices (e.g., compact disc 119, tape, and removablemagneto-optical media (not shown)); and a hard disk 112, or other fixed,high density media drives, connected using an appropriate device bus(e.g., a SCSI bus, an Enhanced IDE bus, or a Ultra DMA bus). Alsoconnected to the same device bus or another device bus, the computersystem 23 may additionally include a compact disc reader 118, a compactdisc reader/writer unit (not shown) or a compact disc jukebox (notshown). Although compact disc 119 is shown in a CD caddy, the compactdisc 119 can be inserted directly into CD-ROM drives which do notrequire caddies.

As stated above, the system includes at least one computer readablemedium. Examples of computer readable media are compact discs 119, harddisks 112, floppy disks, tape, magneto-optical disks, PROMs (EPROM,EEPROM, Flash EPROM), DRAM, SRAM, SDRAM, etc. Stored on any one or on acombination of computer readable media, the present invention includessoftware for controlling both the hardware of the computer 23 and forenabling the computer 23 to interact with a human user. Such softwaremay include, but is not limited to, device drivers, operating systemsand user applications, such as development tools. Such computer readablemedia further includes the computer program product of the presentembodiment according to the invention for detecting condensationpressure of refrigerant; calculating a target condensation pressure ofthe refrigerant necessary for the refrigerant to be an evaporationtemperature in the evaporator; and controlling a condensing unitconnected to the evaporator via a flow distributor so that thecondensation pressure of the refrigerant becomes equal to or more thanthe target condensation pressure.

The computer code devices of the present invention can be anyinterpreted or executable code mechanism, including but not limited toscripts, interpreters, dynamic link libraries, Java classes, andcomplete executable programs.

If the optimization control of condensation pressure is based on anamount of pressure drop required for producing the evaporationtemperature as shown in this embodiment, it is necessary to select aproper distributor 15 for the unit cooler 13 in order to provide aspecified performance. For the selection of a distributor, the liquidrefrigerant temperature at the inlet of the expansion valve 19 has to beestimated. When a two-stage compression freezer unit is used, as in FIG.1, the unit manufacturer is supposed to disclose the liquid refrigeranttemperature at the inlet port of the expansion valve 19, but theinformation is often missing in the manufacturer's catalogues orinformation package. In addition, the condensation temperatures thatmanufacturers publish are restricted to 45° C.-25° C. It means that theestimation of the liquid temperature at the inlet of the expansion valve19 is needed, based on the evaporation and condensation temperatures, ifthe aim is to efficiently operate the system by lowering thecondensation temperature down to approximately −15° C.

For instance, the liquid temperature tm of the refrigerant at the inletof expansion valve 19 is calculated using the following equation:

Equation  1 $\begin{matrix}{{tm} = {\frac{- 120}{to} + {0.275\mspace{14mu}{tk}} + {8.5\frac{V_{L}}{V_{H}}} + {{\frac{\left( {\frac{V_{L}}{V_{H}} + 8} \right)}{10} \cdot \left( {{to} + 30} \right)} \times \left( {1.03 - {0.0025\mspace{14mu}{tk}}} \right)} - {0.15 \cdot \left( {0.5 - \frac{1}{\frac{V_{L}}{V_{H}}}} \right) \cdot \left( {{tk} - 10} \right)} - 31.75}} & (1)\end{matrix}$

Where:

tm=Intermediate Temperature (° C.);

to=Evaporation Temperature (° C.);

tk=Condensation Temperature (° C.);

VL=Displacement volume of the low stage compressor (m3/h); and,

VH=Displacement volume of the high stage compressor ((m3/h).

The condensation temperature, tk, is the temperature of the refrigerantundergoing condensation by the cooling medium.

Equation 1 is the practical equation applicable to when the refrigerantR-22 is used. Other suitable refrigerants can be described with thisequation by modifying the coefficient of the specific heat ratio whentheir respective thermal-physical properties are known. Single-stagecompressors can be designed based on the equation by accounting forover-cooling at a certain constant ratio from the condensationtemperature of the refrigerant. Distributor 15 can be selected bycalculating the liquid temperature of the refrigerant.

A specific example of a selection process is shown here. Table 1 belowshows an example in which a refrigerator has a two-stage compressionfreezer cycle using R-22 as its refrigerant with a displacement ratio of2:1 between high and low stages.

TABLE 1 Winter Summer Season Season Outside Air Temperature −10° C. +25°C. Condensation Temperature (tk) −7° C. +30° C. Evaporation Temperature(to) −41° C. −40.2° C. Liquid Temperature of Refrigerant (tl) −25° C.−10° C. Number of Circuits in the Tubing 20 20 Inner Diameter of Tubing(mm) 3.25 mm 3.25 mm Length of Tubing (mm) 800 mm 800 mm Nozzle Diameter(mm) 4.16 mm 4.16 mm Freezing Capacity (kW) φo 15 kW 12 kW Pressure Dropin the Nozzle 56 kPa 108 kPa Pressure Drop in the Tubing 23 kPa 31 kPaTotal Pressure Drop 79 kPa 139 kPa

In winter, for instance, under the selection criteria of an outsidetemperature at −10° C., refrigerant condensation temperature of −7° C.,refrigerant evaporation temperature at −41° C., liquid refrigeranttemperature at −25° C., the number of circuits in tubing at 20, theinner diameter of tubing at 3.25 mm, tubing length at 800 mm, freezingcapacity at 15 kW, and nozzle diameter at 4.16 mm.

Pressure drop in nozzle 16 . . . 56 kPa

Pressure drop in tubing 17 . . . 23 kPa

Total pressure drop . . . 79 kPa

In this example, the total pressure drop in nozzle 16 and tubing 17 is79 kPa when the condensation temperature tk=−7° C., which is within thedistribution range. In addition, the condensation temperature requiredto set the liquid refrigerant temperature at −25° C. is −7° C., thepressure drop required for evaporation temperature is 390 kPa (abs), atotal of the pressure loss in the liquid piping between the outlet ofthe refrigerant receiver 2 to the expansion valve 19, the pressure dropin the expansion valve, and pressure drops in the distributor nozzle 16and tubing 17. As shown in the right-hand column of Table 1, insummertime when the condensation temperature is higher, the distributor15 is subjected to a pressure drop of 139 kPa. Yet the condensationtemperature is at +30° C., or 1192 kPa (abs) in equivalent pressure,causing no problems in the summer operation even if the distributor isselected in accordance with the minimum criteria for the season, whenthe liquid refrigerant temperature is low.

Table 2 below shows the conditions of the same refrigeration apparatuswhen the temperature in the refrigeration room rises, due to restocking,for example, and the evaporation temperature of the refrigerant alsorises.

TABLE 2 Winter Summer Season Season Outside Air Temperature −10° C. +25°C. Condensation Temperature (tk) −6° C. +30° C. Evaporation Temperature(to) −30° C. −28.9 Liquid Temperature of Refrigerant (tl) −12° C. +3° C.Number of Circuits in the Tubing 20 20 Inner Diameter of Tubing (mm)3.25 mm 3.25 mm Length of Tubing (mm) 800 mm 800 mm Nozzle Diameter (mm)4.16 mm 4.16 mm Freezing Capacity (kW) φo 23 kW 19 kW Pressure Drop inthe Nozzle 108 kPa 190 kPa Pressure Drop in the Tubing 42 kPa 57 kPaTotal Pressure Drop 150 kPa 247 kPa

Table 2 shows that there will be a pressure drop of 150 kPa in totalbetween nozzle 16 and tubing 17 of the distributor 15 in winter. Whenthe freezing capacity increases due to a higher evaporation temperatureof the refrigerant, the required pressure drop for the evaporationtemperature in this example will be approximately 600 kPa, a total ofthe pressure drops in nozzle 16, tubing 17 and expansion valve 19, andthe pressure loss in the liquid piping.

Table 3 shows the condition in which the unit cooler 13 losesperformance due to frost formation.

TABLE 3 Outside Air Temperature −10° C. Condensation Temperature (tk)+10° C. Evaporation Temperature (to) −45° C. Liquid Temperature ofRefrigerant (tl) −20° C. Number of Circuits in the Tubing 20 InnerDiameter of Tubing (mm) 3.25 mm Length of Tubing (mm) 800 mm NozzleDiameter (mm) 4.16 mm Freezing Capacity (kW) φo 12 kW Pressure Drop inthe Nozzle 64 kPa Pressure Drop in the Tubing 25 kPa Total Pressure Drop89 kPa

Normal operation can be maintained by raising the condensationtemperature to +10° C. and obtaining 89 kPa as the total pressure dropin nozzle 16 and tubing 17. In addition, the timing for the defrostingfunction can be automatically determined by monitoring operatingconditions. FIG. 2 shows the relationship between the evaporationtemperature and the liquid refrigerant temperature. In FIG. 2, the xaxis represents tl, the liquid refrigerant temperature (the temperatureat the inlet of expansion valve 19), while the y axis represents thepressure. The solid lines represent the pressure drop under therefrigerant evaporation temperature to −41° C.; the dotted lines, thesame to −30° C. Solid line GA1 and dotted line GB1 show the evaporationtemperature of the refrigerant and also the endpoints of the pressuredrops. Solid line GA2 and dotted line GB2 represent the initial pressureat distributor 15 before a pressure drop; solid line GA3 and dotted lineGB3 represent the endpoint of pressure loss in the liquid refrigerantpiping; and solid line GA4 and dotted line GB4 represent thecondensation pressure limit, which is the aggregate of the pressure dropin expansion valve 19, pressure losses in liquid feeder piping and dryer4, and the pressure drop in distributor 15. Pipe pd shown in the figureshows the pressure loss in the liquid refrigerant piping, while EXP.VΔpshows the pressure drop in the expansion valve.

In this figure, the intersection of the solid line representing therefrigerant evaporation temperature at −41° C. and GA4, the linerepresenting the liquid refrigerant temperature of −25° C., represents395 kPa (abs) (condensation temperature tk=−7° C.) in pressure on thevertical axis. Since the pressure drop is not sufficient if thecondensation temperature goes any lower, this point is taken as thelimit value for condensation pressure. As another example, theintersection of dotted line GB1 representing the refrigerant evaporationtemperature to −30° C. and GB4, the dotted line representing the liquidrefrigerant temperature of −12° C., represents 627 kPa (abs) in pressureon the vertical axis. In other words, the equivalent temperature of+6.6° C. is the limit value for condensation pressure. Thus the pressuredrop is mathematically mapped on the two variables, evaporationtemperature (to) and liquid temperature (tl) of the refrigerant, and anarbitrary constant for variations in freezing capacity to be generatedby the capacity control of the freezing unit is expressed in anequation. The map derived from the polynomial equation or its regressionformula is then installed in the processor so that the condensationpressure optimization controller 23 can control and optimize thecondensation temperature of the refrigerant in the freezing unit.

Table 4 (see page 14) is an example of the map. This map is, forexample, stored in the memory 108 of the controller 23. Actualmeasurements are compared to these calculations so that the condensationperformance is adjusted to approximate the values given.

Table 4 shows a target condensation pressure (kPa) of the refrigerantimmediately upstream of the expansion valve 19. The target condensationpressure is for the refrigerant to be an evaporation temperature in theevaporator. The target condensation pressure is calculated from thefollowing equation:TargetPressure=1125.08+(9.07965*X)+(−0.101693*X*X)+(40.8041*Y)+(1.60973*X*Y)+(0.0177658*X*X*Y)+(−0.0547654*Y*Y)+(−0.00318583*X*Y*Y)+(−0.000044704*X*X*Y*Y),

where X=Evaporation Temperature, and Y=Liquid Temperature of Refrigerant

FIG. 3 is the standard chart of minimum values at which distribution ispossible for the refrigerant R-404a (dew point method) in a two-stagecompression freezing cycle, for which the displacement ratio between lowand high stages is 2.5:1; the evaporation temperature of therefrigerant, −72° C.; and the liquid temperature, −48° C. when thecondensation temperature is −10° C. The solid lines GC1 to GC4 and thedotted lines GD1˜GD4 correspond respectively to the solid lines GA1 toGA4 and the dotted lines GB1˜GB4 of FIG. 2.

As an approach for condensation pressure control, it is certainlypossible to obtain the required pressure drop from the measured valuesof refrigerant evaporation temperature and pressure drop in thedistributor 15. The use of pressure sensors is one way to measure suchpressure drops, but measuring accurate liquid refrigerant temperaturesby the use of refrigerant temperature sensor 26 immediately beforedistributor 15 and at the outlet of tubing 17 of distributor 15 andconverting them to equivalent pressures is by far more accurate andcheaper. It is possible to express a sum of prescribed pressure dropsand pressure losses as well as the pressure drop of the distributor 15in a numerical equation, and to actively lower the refrigerant pressureto the lower limit of condensation pressure for operation. Suchmeasurements are, however, affected by the variable opening of expansionvalve, which in turn affects the control accuracy. It is thereforebetter to utilize this method for verifying pressure drops in theexpansion valve as measured through the evaporation and liquidtemperatures of the refrigerant.

TABLE 4 Program for Condensation Pressure Optimization ControllerTwo-stage Compression Freezer Unit VL/VH 2:1 Evaporation Temperature(to): −20° C.~−45° C. Liquid Temperature of Refrigerant (tl): +1°C.~−20° C. tl ° C. to −20 −19 −18 −17 −16 −15 −14 −13 −12 −11 −10 −45423.0 427.4 431.8 436.2 440.6 445.0 449.4 453.8 458.2 462.6 467.0 −44440.8 445.2 449.7 454.1 458.5 462.9 467.3 471.7 476.1 480.5 484.9 −43457.8 462.2 466.7 471.1 475.6 480.0 484.5 488.9 493.3 497.8 502.2 −42473.7 478.3 482.8 487.3 491.8 496.4 500.9 505.4 510.0 514.5 519.0 −41488.8 493.4 498.0 502.7 507.3 512.0 516.6 521.3 525.9 530.6 535.2 −40507.6 512.4 517.2 522.0 526.8 531.6 536.5 541.3 546.1 550.9 −39 530.9535.9 540.9 545.9 550.9 556.0 561.0 566.0 −38 554.3 559.5 564.8 570.0575.2 580.5 −37 577.9 583.4 588.9 594.5 −36 596.2 602.0 607.8 −35 614.5620.6 −34 632.9 −33 −32 −31 −30 −29 −28 −27 −26 −25 −24 −23 tl ° C. to−9 −8 −7 −6 −5 −4 −3 −2 −1 0 1 −45 471.3 475.7 −44 489.3 493.7 498.0 −43506.7 511.1 515.6 520.0 −42 523.6 528.1 532.6 537.1 541.7 −41 539.9544.6 549.2 553.9 558.5 563.2 −40 555.7 560.5 565.4 570.2 575.0 579.8584.7 −39 571.0 576.0 581.0 586.1 591.1 596.1 601.2 606.2 −38 585.8591.0 596.3 601.5 606.8 612.1 617.4 622.6 627.9 −37 600.0 605.5 611.1616.6 622.1 627.7 633.2 638.8 644.4 649.9 −36 613.7 619.5 625.4 631.2637.1 642.9 648.8 654.7 660.5 666.4 672.3 −35 626.8 633.0 639.2 645.4651.6 657.8 664.1 670.3 676.5 682.7 688.9 −34 639.5 646.1 652.6 659.2665.8 672.4 679.0 685.6 692.2 698.8 705.4 −33 651.6 658.6 665.6 672.6679.6 686.6 693.6 700.7 707.7 714.7 721.7 −32 670.6 678.1 685.5 693.0700.5 708.0 715.4 722.9 730.4 737.9 −31 690.1 698.1 706.0 714.0 722.0729.9 737.9 745.9 753.9 −30 710.2 718.7 727.2 735.7 744.2 752.7 761.2769.7 −29 730.9 740.0 749.1 758.1 767.2 776.2 785.3 −28 752.5 762.1771.8 781.5 791.1 800.8 −27 774.9 785.2 795.5 805.8 816.1 −26 798.3809.3 820.3 831.2 −25 822.9 834.5 846.2 −24 848.6 861.0 −23 875.6

In addition, large unit coolers often have a long ⅝″ tube coil with onecircuit longer than 30 m, despite the fact that they are for cooling.Such unit coolers tend to suffer a significant amount of pressure loss,producing a large pressure differential between the coil inlet andoutlet, resulting in the lower temperature equivalent to evaporationpressure at the outlet rather than the inlet. In other words, thesuction pressure of the freezer unit is low, and the freezing capacityis smaller. If the coil inlet temperature is used as the evaporationtemperature, the real refrigerant evaporation temperature is lower thanthat, resulting in a compression pressure higher than the limit value;hence the control accuracy will be poor. When such a cooler unit is tobe used, a pressure sensor should be installed at the suction pipe ofthe cooler outlet so that the suction pressure equivalent temperature istaken as the evaporation temperature.

If condensation pressure decreases so much that no proper pressure dropsare obtainable, then the refrigerant evaporation temperature falls,which makes TD, the difference between the room and refrigerantevaporation temperatures, deviate from the design values. Thecondensation pressure may be controlled to fall in the proper range byapproximating it to the design TD value prescribed for differentevaporation temperatures. When the room temperature is close to thedesign value, for instance, if superheat is escalating despite theexpansion valve 19 being almost fully open, the condensation pressuremay be controlled to increase.

The refrigerant flow and its basic behavior are described as follows:the over-heated refrigerant gas exhausted from the compressor by aircondenser 8 releases heat to the outside air; the gas is condensed to aliquid refrigerant, which is deposited into refrigerant receiver 2; therefrigerant from the refrigerant receiver 2 is sent to intermediatecooler 3 that chills the refrigerant; the cooled refrigerant is mixed inwith the discharged gas from the low-stage compressor in the freezerunit and sucked into the high-stage compressor; the refrigerant thuscooled goes through expansion valve 19 and distributor 15 in anover-refrigerated state with its pressure dropping down to evaporationpressure; the refrigerant in a two-phase flow at its evaporationtemperature flows through inside the coil of unit cooler 13, and at thesame time, the air on the load side continuously passes the outside ofthe coil; the air is cooled because the refrigerant temperature is lowerthan the air temperature; and, the cooled air is sent out by fan 14 intothe freezer room for cooling. The refrigerant gasified in the coil exitsfrom suction header 18 and is suctioned into the low stage side of thetwo-stage compression freezer unit 1 via suction piping; it is thencompressed again.

In this embodiment, appropriate pressure drop values are calculated byreferencing the liquid refrigerant temperature measured by liquidtemperature sensor 24 as well as the refrigerant evaporation temperaturemeasured by evaporation temperature sensor 25, or the refrigeranttemperature at the inlet of the evaporator coil connected to the tubing17 of distributor 15. This calculation may be performed in rather asimple manner by replacing the two variables, the evaporationtemperature and liquid temperature of the refrigerant, with atwo-variable polynomial equation and by combining the minimum pressuredrop and the smallest pressure drop under an increased evaporationtemperature in a quadratic expression.

The result of this calculation is compared with the measured value ofpressure sensor 28, which is located before the expansion valve 19.Condensation pressure optimization controller 23 generates a controlsignal to inverter 12, instructing it either to step up or step down thecondensation temperature or pressure of the refrigerant in the aircondenser 8. The motor 10 of the air condenser 8 is thereby controlledto regulate the rotation of fan 9, adjusting the refrigerantcondensation performance of the air condenser 8. The condensationpressure optimization controller 23 controls the inverter 12 in such amanner that the actual value measured by pressure sensor 28 approximatesthe calculation result, which is the optimum pressure drop value of therefrigerant.

FIG. 5 shows a flow chart for controlling the condensation pressure.Referring to FIG. 5, at step S2, the liquid temperature sensor 24detects temperature (tl) of liquid refrigerant, the evaporationtemperature sensor 25 detects evaporation temperature (to), and thepressure sensor 28 detects refrigerant pressure Pl before the expansionvalve 19. At step S4, the target condensation pressure Pt is found basedon the map as shown in Table 4 according to the temperature (tl) ofliquid refrigerant and the evaporation temperature (to). Note that thetarget condensation pressure Pt may be calculated according to thefollowing equation:TargetPressure=1125.08+(9.07965*X)+(−0.101693*X*X)+(40.8041*Y)+(1.60973*X*Y)+(0.0177658*X*X*Y)+(−0.0547654*Y*Y)+(−0.0031858*X*Y*Y)+(−0.000044704*X*X*Y*Y),

where X=Evaporation Temperature, and Y=Liquid Temperature of Refrigerant

At step S6, the refrigerant pressure Pl detected by the pressure sensor28 is compared with the target condensation pressure Pt. Then, at stepS8, the controller 23 controls the inverter 12 such that the refrigerantpressure Pl detected by the pressure sensor 28 becomes equal to thetarget condensation pressure Pt. At step S8, the controller 23 maycontrol the inverter 12 such that the refrigerant pressure Pl detectedby the pressure sensor 28 becomes higher, for example, by 20 kPa, thanthe target condensation pressure Pt.

In the operation where the evaporation temperature is the designedevaporation temperature or lower, the condensation pressure optimizationcontroller 23 performs a control function as a safety mechanism asfollows: refrigerant sensor 26 measures the refrigerant temperature atthe inlet of distributor 15, while evaporation temperature sensor 25measures the refrigerant saturation temperature at the outlet ofdistributor 15; the condensation pressure optimization controller 23converts these measured temperatures to respective equivalent pressuresand determines the pressure drop of the refrigerant in the distributor15; this measured pressure drop is compared to the benchmark pressuredrop; if below the benchmark, then the rotation of fan 9 in the aircondenser 8 is controlled by inverter 12; and, the refrigerant pressuredrop in distributor 15 is thus controlled to approximate the benchmarkvalue, which is the optimum value.

As mentioned above, the refrigerant pressure to be measured by pressuresensor 28 located before expansion valve 19 is used as the reference forcontrolling the condensation pressure in the air condenser 8. Thanks tothis configuration, even if pressure losses become significant due toperformance deterioration or choking of dryer 4, air condenser 8 will beoperated at a higher pressure in order to compensate for the loss of thecondensation pressure on the refrigerant side because it is acondensation pressure control based on the liquid refrigerant pressureon the upstream side of expansion valve 19. If, in contrast, thecondenser is placed upstream of the unit cooler, then the pressureproduced by the height of the liquid column will be added to the liquidrefrigerant upstream of the expansion valve, the condensation pressureoptimization controller should add the correction value equivalent tothe liquid column height so that the condensation pressure includes thepressure equivalent to the liquid column height.

As shown thus far, this embodiment will operate by actively lowering thecondensation temperature without ever falling below the pressure dropvalue required for the refrigerant to reach the evaporation temperature.For instance, if a refrigerator described in the aforementioned exampleis operated in the city of Sapporo, annual average freezing performancewill increase by roughly 20% since lower liquid refrigerant temperaturesincrease the specific enthalpy differentials in comparison to theoperation of a typical freezing facility that limits the condensationtemperature of refrigerant at around +25° C. regardless of the outsidetemperature. This allows reductions in operating hours and improvementsin volumetric efficiency of the freezer unit, qu, and the powerconsumption can be reduced by up to approximately 30% through decreasesin the pump power by lower compression ratios. Thus this embodimentproduces a significant savings of 40% or more in power consumption peryear by actively lowering the refrigerant condensation pressure.

The optimized operation method for refrigeration apparatus of thepresent embodiment in which the condensation pressure is determinedbased on the pressure drop in order to reach the evaporation temperaturehas an extremely high precision of distribution in comparison to that ofthe embodiment example 2. For this reason, the temperature difference(TD) between the room and evaporation temperatures of the refrigerant isalso between 3° C. and 1.5° C. This allows the operation to occurthrough convection heat transfer rather than through heat transfer byboiling. Therefore, the method not only suppresses the performancedecline due to frost formation, but also reduces the drying force(sublimation phenomenon), preventing products from drying out. Productscan be frozen and preserved in extremely good condition.

In addition, the present embodiment of refrigeration apparatus alsooffers an advantage that any possible causes for abnormalities can bepromptly eliminated since the upstream liquid pressure of therefrigerant from expansion valve 19 is continuously monitored bypressure sensor 28, which means the condensation temperature of therefrigerant in air condenser 8 is also being monitored.

Although the fans 9 are controlled to adjust the condensation pressurein the above embodiments, an adjustable valve 40 which is provided at anoutput side of the refrigerant of the condensing unit 8 may becontrolled.

Moreover, this invention is in no way limited to the above-mentionedembodiments. Many variations are possible within the scope of thisinvention; including the following examples:

-   -   (1) Although, in the aforementioned embodiment, this invention        is applied to walk-in freezers equipped with a two-stage        compression cycle refrigerating unit, it is equally applicable        to other types of refrigeration and refrigeration apparatus in        general.    -   (2) Although the nozzle type refrigerant distributor is used in        the refrigeration apparatus for the aforementioned embodiment,        this invention is equally applicable to such equipment with a        venturi-type refrigerant distributor if the latter is chosen due        to size considerations.    -   (3) Although a coil air-cooling method is used as the        condensation means in the refrigeration apparatus of the        aforementioned embodiment, this invention is also applicable to        water cooling or evaporation cooling by controlling the water        volume or the fan rotation speed respectively. One variation of        the embodiment is to control a flow rate regulator valve by the        condensation pressure optimization controller so that the        regulator controls the condensation pressure by keeping liquid        refrigerant in the condenser of the embodiment and varying the        size of the cooling condensation area.    -   (4) In the case of flooding-type refrigeration apparatus,        condensation pressure can be optimally controlled simply by the        degree of pressure drop in the refrigerant liquid pipe and the        expansion valve.    -   (5) Since it is possible to control the difference between the        evaporation temperature and the condensation pressure at about        250 kPa even in freezing and refrigeration equipment to be        operated at an evaporation temperature in the vicinity of 0° C.        such as chillers, large power savings can be achieved.    -   (6) In the embodiments, if a gap arises between the design and        actual temperatures of liquid refrigerant, compensation may be        made for the design value of the liquid refrigerant temperature        by obtaining the total pressure drop in the distributor so that        the temperature difference is controlled to remain on or above        the minimum value required for the distributor's operation.    -   (7) In the case of refrigeration apparatus employing        single-stage compressors and operating at a comparatively higher        temperature where the evaporation temperature of the refrigerant        is −30° C. or higher, the optimum control of condensation        pressure can be obtained simply if the amount of overcooling is        taken into consideration at a certain ratio from the        condensation temperature.    -   (8) Although R-22 and R-404 are used in the embodiment, other        refrigerant, for example, R-717, NH3, R-290, propane, R-600 or        butane may be used.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. A refrigeration apparatus comprising: acondensing unit; a flow distributor provided within a unit cooler; anexpansion valve upstream of said flow distributor; an evaporatorconnected to said condensing unit via said flow distributor; a pressuredetector configured to detect condensation pressure of the refrigerant,said pressure detector being located upstream of said expansion valveand downstream of said condensing unit; a refrigerant liquid receiverprovided downstream of said condensing unit and upstream of saidpressure detector; a liquid temperature sensor configured to detect atemperature of the refrigerant at an entrance of the expansion valve; anevaporation temperature sensor configured to detect a temperature of therefrigerant at an exit of the flow distributor; a calculator configuredto calculate a target condensation pressure of the refrigerant necessaryfor the refrigerant to be an evaporation temperature in the evaporator;and a controller configured to control said condensing unit so that thecondensation pressure of the refrigerant becomes equal to or more thanthe target condensation pressure, wherein said condensing unit includesan adjustable valve at an output side of said condensing unit to controlthe flow of the refrigerant, wherein said adjustable valve is provideddownstream of said condensing unit and upstream of said expansion valve,and wherein said controller is configured to control the adjustablevalve, and wherein the controller is configured to calculate an amountof pressure drop in the expansion valve using the temperature detectedby the liquid temperature sensor at the entrance of the expansion valve,and is configured to calculate an amount of pressure drop in the flowdistributor using the temperature detected by the evaporationtemperature sensor at the exit of the flow distributor, and isconfigured to control the condensing unit based on the calculated amountof pressure drop in the expansion valve and the calculated amount ofpressure drop in the flow distributor.
 2. The refrigeration apparatusaccording to claim 1, wherein said condensing unit includes a fan andwherein said controller is configured to control the fan.
 3. Therefrigeration apparatus according to claim 1, wherein said pressuredetector is configured to detect condensation pressure in a vicinity ofand upstream of the expansion valve.
 4. The refrigeration apparatusaccording to claim 1, wherein said calculator is configured to calculatethe target condensation pressure based on the detected temperature ofthe refrigerant at the entrance of the expansion valve and the detectedtemperature of the refrigerant at the exit of the flow distributor. 5.The refrigeration apparatus according to claim 1, wherein saidcontroller is configured to control said condensing unit to increase thecondensation pressure when a degree of superheat of the refrigerantgradually increases even though the expansion valve is fully open. 6.The refrigeration apparatus according to claim 1, further comprising: adryer provided downstream of the refrigerant liquid receiver andupstream of the pressure detector; and an intermediate cooler provideddownstream of the dryer and upstream of the pressure detector.
 7. Therefrigeration apparatus according to claim 1, wherein said adjustablevalve is provided upstream of said refrigerant liquid receiver.
 8. Arefrigeration apparatus comprising: a condensing unit; a flowdistributor; an expansion valve; an evaporator connected to saidcondensing unit via said flow distributor; a pressure detectorconfigured to detect condensation pressure of the refrigerant, saidpressure detector being located upstream of said expansion valve anddownstream of said condensing unit; a refrigerant liquid receiverprovided downstream of said condensing unit and upstream of saidpressure detector; a calculator configured to calculate a targetcondensation pressure of the refrigerant necessary for the refrigerantto be an evaporation temperature in the evaporator; a controllerconfigured to control said condensing unit so that the condensationpressure of the refrigerant becomes equal to or more than the targetcondensation pressure; a compartment temperature sensor configured todetect a compartment temperature in a compartment of the refrigerationapparatus; and an evaporation temperature sensor configured to detect anevaporation temperature, wherein said controller is configured tocontrol said condensing unit according to a change in a differencebetween the compartment temperature and the evaporation temperature, andwherein said condensing unit includes an adjustable valve at an outputside of said condensing unit to control the flow of the refrigerant,wherein said adjustable valve is provided downstream of said condensingunit and upstream of said expansion valve, and wherein said controlleris configured to control the adjustable valve.
 9. The refrigerationapparatus according to claim 8, wherein said difference between thecompartment temperature and the evaporation temperature is at least 1.5°C. and at most 3° C.
 10. A refrigeration apparatus comprising: acondensing unit; a flow distributor provided within a unit cooler; anexpansion valve upstream of said flow distributor; an evaporatorconnected to said condensing unit via said flow distributor; pressuredetecting means for detecting condensation pressure of the refrigerant,said pressure detecting means being located upstream of said expansionvalve and downstream of said condensing unit; a refrigerant liquidreceiver provided downstream of said condensing unit and upstream ofsaid pressure detecting means; a liquid temperature sensing means fordetecting a temperature of the refrigerant at an entrance of theexpansion valve; an evaporation temperature sensing means for detectinga temperature of the refrigerant at an exit of the flow distributor;calculation means for calculating a target condensation pressure ofrefrigerant necessary for the refrigerant to be an evaporationtemperature in the evaporator; and controlling means for controllingsaid condensing unit so that the condensation pressure of therefrigerant becomes equal to or more than the target condensationpressure, wherein said condensing unit includes an adjustable valve atan output side of said condensing unit to control the flow of therefrigerant, wherein said adjustable valve is provided downstream ofsaid condensing unit and upstream of said expansion valve, and whereinsaid controlling means is configured to control the adjustable valve,and wherein the controlling means is configured to calculate an amountof pressure drop in the expansion valve using the temperature detectedby the liquid temperature sensing means at the entrance of the expansionvalve, and is configured to calculate an amount of pressure drop in theflow distributor using the temperature detected by the evaporationtemperature sensing means at the exit of the flow distributor, and isconfigured to control the condensing unit based on the calculated amountof pressure drop in the expansion valve and the calculated amount ofpressure drop in the flow distributor.
 11. The refrigeration apparatusaccording to claim 10, further comprising: a dryer provided downstreamof the refrigerant liquid receiver and upstream of the pressuredetecting means; and an intermediate cooler provided downstream of thedryer and upstream of the pressure detecting means.
 12. Therefrigeration apparatus according to claim 10, wherein said adjustablevalve is provided upstream of said refrigerant liquid receiver.
 13. Amethod for controlling a refrigeration apparatus, the method comprising:detecting condensation pressure of refrigerant at a location upstream ofan expansion valve, downstream of a condensing unit, and downstream of arefrigerant liquid receiver provided downstream of the condensing unit;detecting a temperature of the refrigerant at an entrance of theexpansion valve; detecting a temperature of the refrigerant at an exitof the flow distributor; calculating a target condensation pressure ofthe refrigerant necessary for the refrigerant to be an evaporationtemperature in the evaporator; and controlling the condensing unitconnected to the evaporator via a flow distributor provided within aunit cooler so that the condensation pressure of the refrigerant becomesequal to or more than the target condensation pressure, wherein saidexpansion valve is upstream of said flow distributor, and wherein saidcondensing unit includes an adjustable valve at an output side of saidcondensing unit to control the flow of the refrigerant, wherein saidadjustable valve is provided downstream of said condensing unit andupstream of said expansion valve, and wherein a controller is configuredto control the adjustable valve, and wherein the method furthercomprises calculating an amount of pressure drop in the expansion valveusing the temperature detected at the entrance of the expansion valve,and calculating an amount of pressure drop in the flow distributor usingthe temperature detected at the exit of the flow distributor, andcontrolling the condensing unit based on the calculated amount ofpressure drop in the expansion valve and the calculated amount ofpressure drop in the flow distributor.
 14. The method according to claim13, wherein: a dryer is provided downstream of the refrigerant liquidreceiver and upstream of a location where the condensation pressure ofthe refrigerant is detected; and an intermediate cooler is provideddownstream of the dryer and upstream of the location where thecondensation pressure of the refrigerant is detected.
 15. The methodaccording to claim 13, wherein said adjustable valve is providedupstream of said refrigerant liquid receiver.
 16. A non-transitorycomputer readable medium for storing a computer program, which whenexecuted, controls a computer to perform the steps of: detectingcondensation pressure of refrigerant at a location upstream of anexpansion valve, downstream of a condensing unit, and downstream of arefrigerant liquid receiver provided downstream of the condensing unit;detecting a temperature of the refrigerant at an entrance of theexpansion valve; detecting a temperature of the refrigerant at an exitof the flow distributor; calculating a target condensation pressure ofthe refrigerant necessary for the refrigerant to be an evaporationtemperature in the evaporator; and controlling the condensing unitconnected to the evaporator via a flow distributor provided within aunit cooler so that the condensation pressure of the refrigerant becomesequal to or more than the target condensation pressure, wherein saidexpansion valve is upstream of said flow distributor, and wherein saidcondensing unit includes an adjustable valve at an output side of saidcondensing unit to control the flow of the refrigerant, wherein saidadjustable valve is provided downstream of said condensing unit andupstream of said expansion valve, and wherein a controller is configuredto control the adjustable valve, and wherein the controller isconfigured to calculate an amount of pressure drop in the expansionvalve using the temperature detected by the liquid temperature sensor atthe entrance of the expansion valve, and is configured to calculate anamount of pressure drop in the flow distributor using the temperaturedetected by the evaporation temperature sensor at the exit of the flowdistributor, and is configured to control the condensing unit based onthe calculated amount of pressure drop in the expansion valve and thecalculated amount of pressure drop in the flow distributor.
 17. Thenon-transitory computer readable medium for storing a computer program,which when executed, controls a computer to perform the steps accordingto claim 16, wherein: a dryer is provided downstream of the refrigerantliquid receiver and upstream of a location where the condensationpressure of the refrigerant is detected; and an intermediate cooler isprovided downstream of the dryer and upstream of the location where thecondensation pressure of the refrigerant is detected.
 18. Thenon-transitory computer readable medium for storing a computer program,which when executed, controls a computer to perform the steps accordingto claim 16, wherein said adjustable valve is provided upstream of saidrefrigerant liquid receiver.
 19. A refrigeration apparatus comprising: acondensing unit; a flow distributor; an expansion valve; an evaporatorconnected to said condensing unit via said flow distributor; a pressuredetector configured to detect condensation pressure of the refrigerant,said pressure detector being located upstream of said expansion valveand downstream of said condensing unit; a refrigerant liquid receiverprovided downstream of said condensing unit and upstream of saidpressure detector; a calculator configured to calculate a targetcondensation pressure of the refrigerant necessary for the refrigerantto be an evaporation temperature in the evaporator; a controllerconfigured to control said condensing unit so that the condensationpressure of the refrigerant becomes equal to or more than the targetcondensation pressure; a first temperature detector configured to detecta first temperature of the refrigerant at an inlet of the expansionvalve; and a second temperature detector configured to detect a secondtemperature of the refrigerant at an outlet of the flow distributor;wherein said controller is configured to control the condensing unitbased on calculation of a pressure drop in an expansion device includingthe expansion valve and the flow distributor, the pressure drop beingcalculated by comparing the first temperature of the refrigerantdetected by the first temperature detector and the second temperature ofthe refrigerant detected by the second temperature detector, whereinsaid calculator is configured to calculate a minimum necessary pressuredrop of the flow distributor to allow the second temperature to attainan evaporation temperature in the evaporation device, and to calculate aminimum pressure drop of the flow distributor in an increasedevaporation temperature of the refrigerant, wherein said calculatorcalculates the target condensation pressure from the minimum necessarypressure drop and the minimum pressure drop of the flow distributor inan increased evaporation temperature, wherein said controller isconfigured to control a compression temperature or a compressionpressure of the condensing unit to provide the target condensationpressure, and wherein said condensing unit includes an adjustable valveat an output side of said condensing unit to control the flow of therefrigerant, wherein said adjustable valve is provided downstream ofsaid condensing unit and upstream of said expansion valve, and whereinsaid controller is configured to control the adjustable valve.
 20. Arefrigeration apparatus comprising: a condensing unit; a flowdistributor; an expansion valve; an evaporator connected to saidcondensing unit via said flow distributor; pressure detecting means fordetecting condensation pressure of the refrigerant, said pressuredetecting means being located upstream of said expansion valve anddownstream of said condensing unit; a refrigerant liquid receiverprovided downstream of said condensing unit and upstream of saidpressure detecting means; calculation means for calculating a targetcondensation pressure of refrigerant necessary for the refrigerant to bean evaporation temperature in the evaporator; controlling means forcontrolling said condensing unit so that the condensation pressure ofthe refrigerant becomes equal to or more than the target condensationpressure; a first temperature detector configured to detect a firsttemperature of the refrigerant at an inlet of the expansion valve; and asecond temperature detector configured to detect a second temperature ofthe refrigerant at an outlet of the flow distributor; wherein saidcontrolling means is configured to control the condensing unit based oncalculation of a pressure drop in an expansion device including theexpansion valve and the flow distributor, the pressure drop beingcalculated by comparing the first temperature of the refrigerantdetected by the first temperature detector and the second temperature ofthe refrigerant detected by the second temperature detector, whereinsaid calculation means is configured to calculate a minimum necessarypressure drop of the flow distributor to allow the second temperature toattain an evaporation temperature in the evaporation device, and tocalculate a minimum pressure drop of the flow distributor in anincreased evaporation temperature of the refrigerant, wherein saidcalculation means calculates the target condensation pressure from theminimum necessary pressure drop and the minimum pressure drop of theflow distributor in an increased evaporation temperature, wherein saidcontrolling means is configured to control a compression temperature ora compression pressure of the condensing unit to provide the targetcondensation pressure, and wherein said condensing unit includes anadjustable valve at an output side of said condensing unit to controlthe flow of the refrigerant, wherein said adjustable valve is provideddownstream of said condensing unit and upstream of said expansion valve,and wherein said controlling means is configured to control theadjustable valve.
 21. A method for controlling a refrigerationapparatus, the method comprising: detecting condensation pressure ofrefrigerant at a location upstream of an expansion valve, downstream ofa condensing unit, and downstream of a refrigerant liquid receiverprovided downstream of the condensing unit; calculating a targetcondensation pressure of the refrigerant necessary for the refrigerantto be an evaporation temperature in the evaporator; controlling thecondensing unit connected to the evaporator via a flow distributor sothat the condensation pressure of the refrigerant becomes equal to ormore than the target condensation pressure; detecting a firsttemperature of the refrigerant at an inlet of the expansion valve; anddetecting a second temperature of the refrigerant at an outlet of theflow distributor; wherein the condensing unit is controlled based oncalculation of a pressure drop in an expansion device including theexpansion valve and the flow distributor, the pressure drop beingcalculated by comparing the first temperature of the refrigerantdetected by the first temperature detector and the second temperature ofthe refrigerant detected by the second temperature detector, wherein thetarget condensation pressure is calculated from a minimum necessarypressure drop and a minimum pressure drop of the flow distributor in anincreased evaporation temperature where the minimum necessary pressuredrop of the flow distributor is calculated to allow the secondtemperature to attain an evaporation temperature in the evaporationdevice, and the minimum pressure drop of the flow distributor iscalculated in an increased evaporation temperature of the refrigerant,wherein the condensing unit is controlled to provide the targetcondensation pressure by controlling a compression temperature or acompression pressure of the condensing unit, and wherein said condensingunit includes an adjustable valve at an output side of said condensingunit to control the flow of the refrigerant, wherein said adjustablevalve is provided downstream of said condensing unit and upstream ofsaid expansion valve, and wherein a controller is configured to controlthe adjustable valve.
 22. A non-transitory computer readable medium forstoring a computer program, which when executed, controls a computer toperform the steps of: detecting condensation pressure of refrigerant ata location upstream of an expansion valve, downstream of a condensingunit, and downstream of a refrigerant liquid receiver provideddownstream of the condensing unit; calculating a target condensationpressure of the refrigerant necessary for the refrigerant to be anevaporation temperature in the evaporator; controlling the condensingunit connected to the evaporator via a flow distributor so that thecondensation pressure of the refrigerant becomes equal to or more thanthe target condensation pressure; detecting a first temperature of therefrigerant at an inlet of the expansion valve; and detecting a secondtemperature of the refrigerant at an outlet of the flow distributor;wherein the condensing unit is controlled based on calculation of apressure drop in an expansion device including the expansion valve andthe flow distributor, the pressure drop being calculated by comparingthe first temperature of the refrigerant detected by the firsttemperature detector and the second temperature of the refrigerantdetected by the second temperature detector, wherein the targetcondensation pressure is calculated from a minimum necessary pressuredrop and a minimum pressure drop of the flow distributor in an increasedevaporation temperature where the minimum necessary pressure drop of theflow distributor is calculated to allow the second temperature to attainan evaporation temperature in the evaporation device, and the minimumpressure drop of the flow distributor is calculated in an increasedevaporation temperature of the refrigerant, wherein the condensing unitis controlled to provide the target condensation pressure by controllinga compression temperature or a compression pressure of the condensingunit, and wherein said condensing unit includes an adjustable valve atan output side of said condensing unit to control the flow of therefrigerant, wherein said adjustable valve is provided downstream ofsaid condensing unit and upstream of said expansion valve, and wherein acontroller is configured to control the adjustable valve.